Modular Digital Backends for Microwave Radiometry
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ElectroScience Lab November 2002 ElectroScience Laboratory, The Ohio State University 1320 Kinnear Road, Columbus OH 43221 USA { hampson.8, ellingson.1 }@osu.edu Modular Digital Backends for Microwave Radiometry Grant Hampson Steve Ellingson
Transcript of Modular Digital Backends for Microwave Radiometry
ElectroScience Lab
November 2002
ElectroScience Laboratory, The Ohio State University1320 Kinnear Road, Columbus OH 43221 USA
{ hampson.8, ellingson.1 }@osu.edu
Modular Digital Backendsfor Microwave Radiometry
Grant HampsonSteve Ellingson
ElectroScience Lab
Overview
l OSU/ESL has a NASA contract to develop a wideband coherentdigitizing radiometer with built-in RFI mitigation for earth remotesensing at L-band
l We have chosen a development strategy which emphasizes modularimplementation of functions using FPGAs on interconnecting PCBs
l Advantages:– System can be reconfigured by rearranging modules– Modules are reuseable (analogous to “reuseable software”)– Facilitiates a “test-as-you-go” approach (risk mitigation)– System-level testing possible in early stages of design– Less waste (replace only parts of system that don’t work, or need
updating)l These designs / design methods maybe useful in the development of
future radio astronomy backendsl Design details from this effort are freely available
ElectroScience Lab
System Block Diagram
Data Recording/Control
Low-noisefront end
AnalogDownconverter
Digital IF(DIF)
ADC
Asynchronous Pulse Blanker (APB)
1K FFTFrequency domain
blanker
Integration(SDP)
200 MSPS10 bits
80 MHz BW@ 150 MHz
50 MHz BW@ +25 MHz100 MSPS16+16 bits
FPGA
FPGA FPGA
FPGA
(In Progress)
CaptureBoard
FIFO
(In Progress)50 MHz BW@ -25 MHz100 MSPS16+16 bits
ΣΣ
Low Rate Data to PC
PC
ElectroScience Lab
RFI-Robust Total-Power Radiometer Backend
l Functional blocks on separate boards for rapid development/evaluation
l Each block controlled by a “Rabbit” µC via TCP/IP
ADC DIF APB FFT CaptureSDP
ElectroScience Lab
Digital IF (DIF) Module
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Asynchronous Pulse Blanker (APB)
l Maintains a running estimate of mean & variance of incoming time series
l Sample mag. > β standard deviations above the mean triggers blanker
l Blanking operates on down-stream data exiting a FIFO
l Signals before and after trigger are blanked
ElectroScience Lab
FFT ModuleFFT’s implementedusing Altera FFT libraries,includes windowing
Many tradeoffs possible
Currently:(1) 1 Complex FFT (1 FPGA)1K points, 14 bits, 19% duty cycle(2) 2 Complex FFTs (1 FPGA)1K points, 10 bits, 33% duty cycle
Soon:8 Complex FFTs (2 FPGAs)1K points, 14 bits, 100% duty cycle(shown)
ElectroScience Lab
Field Demo: Time Blanking of ATC Radar
l Observations using a low gain discone antenna on ESL roof
– 1306 +/- 50 MHz using DIF (1 sideband) + APB + FFT + SDP
– Spectra integrated over 42 ms (4096 FFTs)
ATC radar at1331 MHz clearlyvisible
APB off
APB on
ElectroScience Lab
Field Demo: Time Blanking of ATC Radar
l Time domain results:
l Effect of varying APB threshold in frequency domain:
Direct path Multipath
APB “Blanking”decision
“Max held” spectra
Averaged spectra
ElectroScience Lab
Why Low-Gain Receivers with Digital Filters are Nice:
l No calibration, temperature control, or Dicke switching of any kindl Variance vs. integration time follows theoretical curve through
6 orders of magnitude (3 orders of magnitude sensitivity improvement)l Actual elapsed time for this observation was 14 minutes
(100 seconds of integrated data.)
ElectroScience Lab
For More Information
l http://esl.eng.ohio-state.edu/~swe/iip/docserv.html
(E-mail [email protected] for a username & password)
